[clang] [CIR] Fix union RecordType::getTypeSizeInBits to return bits (PR #191516)

[Erich Keane via cfe-commits]

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@@ -378,8 +378,12 @@ PointerType::getABIAlignment(const ::mlir::DataLayout &dataLayout,
 llvm::TypeSize
 RecordType::getTypeSizeInBits(const mlir::DataLayout &dataLayout,
                               mlir::DataLayoutEntryListRef params) const {
-  if (isUnion())
-    return dataLayout.getTypeSize(getLargestMember(dataLayout));
+  if (isUnion()) {
+    mlir::Type largest = getLargestMember(dataLayout);
+    if (!largest)
+      return llvm::TypeSize::getFixed(0);
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erichkeane wrote:

Agreed, it definitely SHOULD be with sizeof.  But that is a compile-time expression generated by the frontend, so size being 0 here looks odd...

I have a patch that does a bit of rewrite on union sizes (we're getting it not-so-subtly wrong) that I'm preparing, but i saw this while writing it and am not sure if this is right. 

https://github.com/llvm/llvm-project/pull/191516